Shoe stiffener



Patented Oct. 1,1940

UNIT D STATES PATENT OFFICE SHOE STIFFENER Richard Almy, Lancaster, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania 4 No Drawing. Application April 27, 1938, Serial 4 Claims.

I 5 the application of heat, so that in the lasting operation in the manufacture of shoes, the blank is molded about and takes the shape of the toe end of the last, and on cooling retains such shape.

A shoe stiffener should be hard, resilient and flexible so that it will impart to a shoe a maximum degree of firmness and yet not be brittle, so that when subjected to a deforming pressure, it will resume its original shape upon removal of the pressure. A stiffener should adhere to adjacent 5 parts of a shoe to form a unitary structure but such adhesion should not be accompanied by staining. To fit in the rapid routine of modern shoe manufacture; stiffener blanks must be adapted to be tempered or rendered soft quickly, and

when in such condition, they must be capable of being wiped over or lasted with little effort on the part of the operator. In order that a shoe will keep its sh'ap,'the stiffening material in a blank should be resistant to temperatures ordinarily. encountered in storewindows and wear. A satisfactory stiffener need possess the above mentioned desirable qualities and still be so economical in cost as to permit its universal applicationto all types of shoes.

Various attempts have been madeto produce box toes possessing the above enumerated quali ties. All such attempts, however, have resulted in failure or have had various disadvantages assosaturate or impregnate a base or foundation, butresulted in a commercially unacceptable product. The product was stifi, brittle and inflexible since the continued milling of the, rubber destroyed its 5 resiliency; consequently, the blank'possessed only those qualities inherent in a. thermoplastic stiffener, that is, it was susceptible to low tem eratures, and when cooled was brittle, hard, fr able, and inflexible. The continued high temperatures used in the melting and milling operations destroyed the resilient qualities of the rubber and thus prevented the attainment of a flexible and resilient material. The stiffening compound was extremely viscous and only incomplete ,or partial saturation of the base or foundation could be effected.

This invention has for its chief object to obviate the disadvantages inherent in such stifieners and the methods of making them. An object of my invention is to provide a shoe stiffener which possesses not only inherent properties of stiffness, rigidity, flexibility and resiliency when cold, and of being made limp or plastic when heated to a moderate temperature not injurious to leather, but which is practicable and economical in com-- mercial manufacture. A further object is to provide a method of making such shoe stiifeners which is rapid and efiicient in operation; which requires a minimum expenditure for commercial plan and which may be practiced without difficulty by comparatively unskilled labor:

In the present invention, I employ a stiffening compound composed of dispersions of acidic resins, gums, waxes, bitumens or other waterrepellent thermoplastic substances of acidic nature in which rubber latex, or other rubber dispersions, is intermixed and dispersed. The stiff-- m'ng compound is so prepared that a homo geneous mixture is formed having a melting or softening point at a moderate temperature, say F. to F., whichis not injurious to the leather components of a shoe, and yet which sets rapidly when cooled. A bibulous base or'founda- 'tion, such as felt, paper, cotton flannel or canvas duck, may be impregnated or saturated with the; stiffening compound, and'for'med into shoe stiffening blanks of appropriate size and shape. I have found it is essential to add a protective agent, such as a casein solution, to the latex in order that it may be dispersed in the acidic dispersion and stabilized against separation...

I have also found it essential to add an acidic substance to the casein-latex solution before it is admixed with the acidic dispersion to neutralize the alkaline nature of the solution, thereby .pre- ,venting the formation of a. resin soap by. the reaction between the alkaline constituents of thelatex and the acid constituents'of the resin when compound is used in the manufacture of shoe stiffeners.

In order that my invention may be readily understood, I will describe a preferred embodiment thereof. A satisfactory stiffening compound can be made by the following formula:

It will be appreciated when the saturant prepared according to the above formula has been dried, it will comprise the ingredients in approximately the following proportions: Rubber 10%, limed rosin 35%, and rosin 55%.

In the preparation of the stiffening compound, the latex is conditioned in order that it may be dispersed in .the resin and stabilized against separation when the product is heated. To this end, a paste of water, ammonia and a water-carrying colloid such as casein is prepared. A small amount of preservative such as Thymol," a preservative for casein well-known in the industry, may be added to the solution if desired. Such solution is added to the latex and thoroughly mixed therewith. The solution is rendered acidic by mixing sufficient commercial formalin therewith until the solution 'is faintly acidic to litmus paper. It will be appreciated the amount of formalin necessarily varies with variations in the ammonia content of the preserved latex, sufficient formalin being added to neutralize the ammonia content of the preserved latex.

To prepare the rosin dispersion, approximately 55 parts by weight of rosin are ground in approximately 55 parts by weight of water by means of a ball mill for a sufficient time to finely divide the rosin in minute particles ranging from one micron to perhaps 30 microns in size and averaging about seven microns. Such a dispersion is only temporarily stable but may be used if continuous stirring is carried on. Preferably,

about 5 /2 parts by weight of stabilizing agents, such as the sodium salt of isopropyl naphthalene sulfonic acid known commercially as Aquarex F, are added to stabilize the dispersion. The limed rosin dispersion may be made in the same manner, using approximately 60 parts by weight of limed rosin, 34 parts of water and six parts of stabilizing agents. If desired in order to lower the time required to prepare the dispersion, such dispersions may be prepared together. That is, the resins may.be ground together in water to form a dispersion rather than' prepared as separate dispersions and admixed. It will be appreciated resin dispersions prepared as abovedescribed may contain a high percentage of the dispersed materials without causing the dispersion to be highly viscous in contradistinction to methods of preparing resin emulsions.

The resin dispersions are added to the latexcaseinsolution and thoroughly mixed therewith so that the latex solution is dispersed uniformly throughout the mixture. The compound may be used immediately or may be placed in air-tight cans until it is requiredfor use. I

The bibulous base or foundation is saturated or impregnated with the stiffening agent by passing a web of the material through a saturating tank, the excess saturant being removed by drawing the web through squeeze or pressure rods or rolls. The web is then dried by placing it for thirty minutes in a stove or oven heated to approximately 250 F., the stiifening compound being deposited in the interstices of the web and on the surface thereof by evaporation of the aqueous vehicle. Box toe blanks of a desired size and shape are then died or cut out of the web, and are skived-to form thin or tapered edges. Such blanks are resilient, 'tough, rigid and flexible when cold, and are capable of being rendered easily moldable by the application of heat. They are not friable and the thermoplastic material does not powder or give oif dust when the blanks are skived or bent.

When it is desired to assemble a shoe, the box toe blank is heated at moderate temperature, roughly, 140 F. to 185 F. depending upon the melting point of the thermoplastic agent and is thereby rendered soft and flexible so that it may be drawn and molded in the pulling over and bed-lasting operation. When the molded box .toe has set, it is again resilient, tough, flexible and hard and is able to resume its shape after a deforming pressure thereon has been removed.

It will be understood it is extremely difflcult or impossible to make a substantially homogeneous compound of rosin, limed rosin and latex unless the latex be conditioned to permit it to be dispersed in the acidic resin and stabilized against separation when the product is heated. I have found that when normal ammonia preserved latex is used in such compound, the ammonia content of the latex reacts with the acid it is impossible to impregnate the base or foundation with such compound and hence the box toe blank does not possess the properties required for satisfactory use. I have overcome this problem by adding suificient formalin to the latex-casein solution to neutralize the ammonia content of the preserved latex solution or to render it faintly acidic rather than alkaline and consequently, when the solutions are intermixed such undesirable reaction is obviated and the stiffening compound so formed is satisfactory in all respects.

If desired, vulcanizing ingredients may be added to the latex in sufficient quantity to vulcanize the rubber during the drying operation or the rubber particles may exist in vulcanized form in the latex. Other protective agents, such as glue, soaps, starch, water soluble gums or the like may be substituted for the casein. Other acidic substances such as formic acid or acetic acid solutions may be substituted for formalin to neutralize the ammonia content of the latex. My invention is-not confined to the use of dispersions of rosin and/or limed rosin since dispersions of other acidic thermoplastic substances may be substituted therefor.

This invention provides a shoe stiffener which is hard, resilient and flexible so that it will impart to the shoe a maximum degree of firmness and yet not be brittle, so that when subjected to a deforming pressure, it will resume its original shape upon removal of the pressure. When inserted in a shoe it will adhere to adjacent parts thereof to form a unitary structure but such adhesion is not accompanied by objectionable staining. It may be tempered quickly and is capable of being lasted with little effort on the part of the operator. It is economical in manufacture and does not require excessive expendiunderstood my invention is not so limited but may be otherwise embodied within the scope of the following claims.

I claim:

1. As an article of manufacture, a normally stiff resilient shoe stiffener blank adapted to be rapidly rendered soft and plastic by the application of moderate heat, comprising a readily permeable fibrous foundation carrying within its interstices and on its surface the dried residue of a homogeneous dispersion of an acidic thermoplastic substance, an alkaline preserved rubber, a protective agent coating the dispersed particles of rubber, and an acidic substancerendering said rubber faintly acidic, said acidic thermoplastic substance being present in sufliclent quantityv to impart to said stiffener plasticity under the application of moderate heat, and said rubber being present in sufficient amount to enhance the resiliency and flexibility of the stiifener while substantially maintaining the thermoplasticity thereof.

2. As an "article of manufacture, a normally stiff resilient shoestifiener blank adapted to be readily rendered soft and plastic by the application of moderate heat, comprising a readily permeable fibrous foundation carrying within its interstices and on its surface the dried residue of a homogeneous mixture including a, rosin dispersion, rubber latex, a/ casein solution protecting the rubber particles of said latex, and an acidic substance rendering said latex faintly acidic, said rosin being present in sufficient quantity to impart to said stiffener plasticity under the application of moderate heat, and said rubber being present in suflicient amount to enhance the resiliencyand flexibility of the stiifener while substantially maintaining the ther-' moplasticity thereof.

3. An article of manufacture according to claim 2, in which said acidic substance comprises formalin.

4. A base fabric adapted for the manufacture of normally stiff, resilient shoe stiffener blanks, comprising a readily permeable fibrous base carrying a homogeneous aqueous dispersion of rubber, rosin, limed rosin, a protective agent coating the dispersed particles of rubber, and an acidic sub-stance rendering said rubber faintly acidic, said rosin and' limed rosin being present in said dispersion in the form of minute particles ranging from one micron to thirty microns in size, and being adapted to be de posited within the interstices of the base and on the surface thereof by evaporation of the aqueous vehicle.

RICHARD ALMY. 

